The present invention relates to plasma sources for use in the performance of plasma-assisted processes, including deposition and etching processes performed on substrates in processing chambers. The invention particularly relates to plasma sources which allow processing of large area substrates.
There is a demand for plasma sources that will enable processes of the above-mentioned type to be performed on large size wafers and even more so for flat panel display processing. There are indications in the industry that efforts will be made to manufacture flat panel displays measuring 1 meter on a side and plasma-assisted processing of such substrates will require higher plasma ion density levels than are produced in existing systems. Plasma-assisted processing of such large area substrates requires both high plasma density and high pumping speed to achieve high processing rates.
In plasma sources of the type described above, the plasma deposition or etching rate will depend on the ion flux, or ion density, as long as the process gas throughput, or pumping speed, satisfies the processing chamber requirements. Therefore, the achievement of satisfactory processing rates for large area substrates requires both the gas throughput and the ion flux be sufficiently high.
In addition, a plasma source having the requisite large dimensions must withstand a considerable force from atmospheric pressure and must be capable of providing an optimum geometry for creation of an electric field that will provide a uniform plasma inside the processing chamber of the source.
It is an object of the present invention to provide a large area plasma source which has the above-mentioned capabilities.
Another object of the invention is to provide a large area plasma source housing capable of supporting atmospheric pressure forces while providing a requisite electrostatic shield for the plasma confined within the housing and permitting transmission of RF electromagnetic field energy to the plasma.
The invention achieves these and other objects by providing a plasma source housing having side walls made of: metal electrostatic shield members that provide support against atmospheric pressure; or a ridged dielectric wall that is capable of supporting atmospheric pressure and is combined with electrically conductive elements that provide the electrostatic shield function; or a combination of the two. These walls can be shaped according to any vertical geometry including, but not limited to, straight, tapering in or out, curved in or out, etc. Therefore, a plasma source housing can be constructed to have virtually any dimensions and shape needed, while allowing RF energy to be supplied to the plasma through the housing wall. In addition, this housing will readily accommodate a system for cooling the processing chamber walls.
A further object of the invention is to achieve a high degree of plasma uniformity within the processing chamber. Because the RF electric field which creates and maintains the plasma originates in the region which surrounds the processing chamber, plasma uniformity is attained by diffusion, with gas species, or processing gas, flow and plasma gradient combining to provide process uniformity. Therefore, at any pressure and RF power level, plasma uniformity is a function of the aspect ratio of the processing chamber, i.e., the ratio of the square root of the cross sectional area to the height of the processing chamber. The cross-sectional area is the area of a horizontal plane at a location where the chamber has an average cross-sectional area.
It presently appears that by applying the principles to be disclosed herein together with standard testing procedures, a high degree of plasma uniformity can be achieved.
The above and other objects are achieved, according to the present invention, by a chamber housing enclosing a plasma region in a large area plasma source used for performing plasma assisted processes on large area substrates, the chamber housing comprising:
a housing member constituting a substantially vertically extending wall surrounding a space corresponding to the plasma region, the housing member having a plurality of openings, and electrically conductive elements forming an electrostatic shield around the space;
a plurality of dielectric members each having a peripheral edge and each disposed to close a respective opening; and
sealing means forming a hermetic seal between the housing member and the peripheral edge of each of the dielectric members.